Horseradish peroxidase (HRP) was injected into the subthalamic nucleus in rat brain by means of microiontophoresis. The animals were allowed to survive 24 to 36 hours in order for uptake and transport to nerve cell bodies to occur. The brains were cut and processed using tetramethylbenzidene to visualize the HRP. Labelled cell bodies were found principally in globus pallidus and in the compacta region of subtantia nigra, suggesting significant inputs from these regions. Scattered labelled cells were also located in frontal cortex and zona incerta. The input from substantia nigra is consistent with a dopaminergic afferent connection to subthalamic nucleus.